Solar for Paper and Packaging Plants: Sizing, Roof, Approvals and Payback (50 kW+)

A paper or packaging plant should size solar from its daytime bill, not from its roof. Take the daytime kWh your corrugator, printing and utility loads already use, check sanctioned load and transformer headroom, then fit the plant to the smaller of those and the usable roof. Up to 500 kW this normally runs under net metering; above that, captive or open access rules apply.

Size the plant from the bill, not the roof

Four numbers decide the size, and the smallest one wins.

As a planning figure for north India, each kW generates about 120 units a month. A 100 kW plant therefore gives about 12,000 units a month. Compare that with your daytime use. If the plant is smaller than your weekday daylight load, nearly every unit is used on site, which is where solar earns its saving most reliably. Test sizes in the solar calculator and check area in the plant area calculator.

What is specific to paper and packaging plants

Most of the sizing method is the same as for any factory. These points are particular to this sector. They are engineering considerations to check on your site, not statistics.

• Load shape. A mill that runs its process around the clock uses daytime power every day. A corrugated-box or printing converter on one or two shifts uses it on working days and exports on weekly offs. Read the shift calendar before sizing.
• Large single-span roofs. Pre-engineered sheds give long, clean roof runs, which is good for layout. Check purlin spacing, sheet condition and fixings, and skylights that remove usable area. See the roof load calculator and our note on older roofs.
• Dust, fibre and deposits. Paper dust, lint and boiler stack deposits settle on modules and lower output. Plan walkway access, a cleaning routine and inverter locations away from dusty bays.
• Fire load. Reel, board and waste-paper storage carries a high fire load. Rooftop DC wiring, isolators, cable routing and firefighter access need design attention. Read rooftop solar DC fire safety, and share the layout with your insurer and fire officer.
• Shading from stacks and vents. Chimneys, steam plumes, exhaust ducts and cooling equipment cast shadows that a flat drawing misses. A shadow study should come before the design. Why estimates differ is explained in our shading note.
• Drives and harmonics. Plants with many variable-speed drives need a power-quality check with the inverters. See harmonics and inverters.
• Boiler and DG interlocks. If you run captive boilers, co-generation or DG sets, the solar changeover logic must be designed in. See solar, DG and grid switching.

Which approval route applies by size

The central net-metering limit was raised to 500 kW by a 2021 amendment to the Electricity (Rights of Consumers) Rules. The Green Energy Open Access Rules, 2022 lowered the open access limit for green energy from 1 MW to 100 kW. Under Rule 3 of the Electricity Rules, 2005, a captive plant needs its users to own at least 26% and consume at least 51% of its annual generation. State regulations then set the details, so confirm each point with your DISCOM. Our open access solar page compares the routes. For sizes, see the pages for 100 kW and 500 kW.

Payback: the logic and a worked range

Cost comes from the published C&I band of ₹24,000–32,000 per kW excluding GST. Savings come from the energy charge you avoid on each self-used unit. Solar does not normally reduce fixed or demand charges, so do not use the whole bill. Divide cost by yearly savings, less maintenance.

Illustration for a 200 kW plant, so the arithmetic is visible. At mid-band (₹28,000 per kW) the cost is ₹56 lakh excluding GST. Generation is 200 x 120 x 12 = 2.88 lakh units a year. The avoided rate is a blended ₹9 per unit, the figure the published size pages use; replace it with your own. Maintenance is taken as 1% of cost a year, and exported units are valued at zero to be cautious.

These figures ignore GST, tax benefits, module degradation and tariff changes, and a different roof or HT works scope will move the cost. Use the payback calculator with your own bill.

Questions to settle before you tender

A paper or packaging plant gets better quotations when the brief names the sector's risks. Put these in the RFQ so bidders price the same scope.

• Which lines and shifts run on weekdays, Sundays and holidays, and what is the lowest weekday and weekend load in daylight?
• Where are the stacks, vents, steam plumes and exhaust ducts, and which roof sections do they shade at which hours?
• Who owns the roof, what is its age and sheet type, and is there a structural report or load figure?
• What is the cleaning method and frequency for dust-laden bays, and who carries it in the maintenance scope?
• What has the insurer asked for on rooftop DC wiring, isolators and access, and what will the fire officer need to see?
• Who files the DISCOM application and the Electrical Inspector's file, and who pays the fees and arranges the meter?

Our guide to evaluating solar EPC proposals shows how to line up bidders on the same basis.

How Secured Engineers helps

Secured Engineers designs solar plants in-house and files the CEIG and DISCOM net-metering applications in-house. MEPF and solar can sit under one contract, which helps where a plant also needs fire fighting or electrical upgrades alongside the array. The company works from offices in Noida (Delhi NCR) and Ludhiana, with 535+ projects across 18+ states and 89.77% repeat clients.

Start from our solar for factories page, or send your twelve bills and a roof photograph on WhatsApp, call +91 70099 85817, or ask for a free proposal.